Weight-matched set of golf clubs

ABSTRACT

A weight matched set of golf clubs is provided, wherein each club provides the golfer with precisely the same feel when the club is swung. Weight is added to each of the golf clubs in a set whose rotational dynamic properties (e.g., moment of inertia) have been matched about a selected axis. Sufficient weight is added to each of the clubs in the set to make the total weight of that club equal to the total weight of the heaviest club in the set. Such weight is added in such manner as to leave the moment of inertia about the selected axis of each club in the set essentially unchanged. This will provide the golfer with a set of clubs whose translational inertia, as well as the previously established rotational inertia, is essentially the same for each club in the set.

RELATED APPLICATION

The present application claims priority of U.S. Patent Application Ser. No. 60/668,467 filed by Alan L. Brooks on Apr. 4, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to providing a matched set of golf clubs that all have the same feel when used by a golfer by rendering each club to have the same total weight without substantially changing the rotational dynamic properties of the clubs or the flexural properties of the shaft in each club.

2. Description of Related Art

The action taken by a golfer in striking the ball can be characterized as having four parts. The first part is the ‘address of the ball’ wherein a stationary position is assumed by the golfer and the club head is placed in some relation to the ball. The second part is the ‘backswing’ wherein the club is taken from the address position to a position generally above and behind the shoulders of the golfer where the club is poised to strike the ball. The third part is the ‘downswing’ where the club is used to strike the ball and the fourth part is the ‘follow through’ where the golfer and club are brought back to a stationary position following the striking of the ball.

For years, golfers have tried to improve their game by searching for the ideal set of golf clubs, wherein each club ‘feels’ the same and performs in a consistent manner. As such, numerous methods have been formulated in the attempts to dynamically match a set of golf clubs. Many systems have been developed that match the dynamics of one club in a set to the dynamics of other clubs in the same set.

One such method for matching the dynamics of golf clubs in a set is to provide the set with the same moment of inertia with respect to a common swinging axis. Such a method is disclosed in U.S. Pat. No. 3,698,239 issued to Everett, III. This method uses the assumption that having identical moments of inertia per club will inherently provide the golfer with better feel and more control. An attempt to provide a method for producing a set of moment of inertia matched clubs is disclosed in U.S. Pat. No. 1,953,916 issued to Adams.

The commonly used “Lorythmic Swing Weight Scale” defines a ‘swing weight’, which approximates the moment of inertia about an axis at the grip end of a club. This approximation is performed by measuring the static moment about a fulcrum point which is established at a specified distance from the grip end of the club. Note that swing weight is not a measurement of the moment of inertia, but rather an estimation of the moment of inertia. Also note that swing weight is a valid approximation of moment of inertia only over a relatively narrow range of club design parameters.

FIG. 1 is a diagram illustrating the manner in which the swing weight of a golf club 100 is determined. Golf club 100 includes shaft 101, head 102 and grip 103. The swing weight SW is determined by supporting the shaft 101 at a fulcrum point F, and measuring the moment required to statically balance the club. The fulcrum point F is located a precise distance (i.e., 14 inches) from the grip end of the club. As mentioned above, the swing weight is an approximation of the moment of inertia of the club 100 around an axis A at the grip end 104 of the club.

Swing weight is expressed as a combination of a letter (A, B, C, D, E, F) and a number (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). Each combination of letter and number is known as a ‘swing weight point’. Thus, there are 77 possible swing weight points. The lightest swing weight is AO, and the heaviest swing weight is G10. Most men's golf club sets are manufactured with a swing weight of D0 or D1, while most women's golf club sets are manufactured with a swing weight of C5 to C7. Each golf club in a set is manufactured to have the same swing weight.

In order for each golf club in a set to have the same swing weight, the weight of the golf club head 102 must decrease as the length of the golf club shaft 101 increases. Successive clubs in a set typically vary in shaft length by 0.5 inches and club head weight by 7 grams, with longer clubs having a lighter head weight. For example, if a 9-iron of a set has a length of L, and a club head weight W, then the 8-iron of the same set typically has a length of L+0.5 inches and weight of W−7 grams. The total weight of successive clubs in a set varies by about 5 grams. As club head weights increase by 7 grams, the correspondingly shorter shafts decrease in weight by about 2 grams. For this reason, each of the golf clubs of a set will have a different total weight. For example, a 3-iron may weigh 30 grams less than a 9-iron from the same set. This effect is amplified for a driver (or any other wood), which typically has a longer and lighter shaft. For example, a driver having a 45.5 inch graphite (carbon composite) shaft may have a total weight of about 310 grams, which is about 130 grams lighter (about 30% lighter) than a steel shafted 9-iron of the same set. In virtually all sets of golf clubs currently produced, the weight of each individual club varies substantially from every other club in the set.

With a matched swing weight, each of the golf clubs in a set will ‘feel’ similar during phases of the swing where the club head swings (i.e., rotates) about the axis A at the grip end of the shaft. The main phase of the swing where the club head swings about the grip end of the shaft exists during the final phase of the downswing, immediately before (and after) the club head makes impact with the golf ball. During this phase of the downswing, the golfer's arms are extended, and the club head swings about an axis created by the golfer's wrists. This axis point substantially coincides with the axis A at the grip end of the shaft. This phase of the downswing is hereinafter referred to as the ‘release’, because the club head is ‘released’ to swing about the wrists.

However, the golf swing is a very complicated movement, which includes movements other than the above-described ‘release’ phase of the downswing. Other common movements in the golf swing include the backswing, the initial phase of the downswing and the follow-through. Swing weight is a poor approximation of how the club ‘feels’ during much of these other swing movements, because the primary movement of the club head is not a rotating movement about a fixed axis during these other swing movements. For example, during the last phase of the backswing and the initial phase of the downswing, the golf club is translated by the hands and rotates very little. FIG. 2 illustrates one example of translational movement of golf club 100 along axis T. Unfortunately, there is a significant difference in the translational inertia (i.e., weight) of the various golf clubs in the set. For this reason, a 9-iron and a driver having the same swing weight will ‘feel’ very different during the last phase of the backswing and the initial phase of the downswing. This difference in ‘feel’ may cause golfers to apply different swings to different golf clubs of the same set. That is, the difference in ‘feel’ often causes golfers to swing the 9-iron in a different manner than they swing the driver (or other clubs of the same set). This undesirably introduces additional complexity to an already complex series of movements.

As described above, swing weight matching was developed as an approximation of moment of inertia matching. Swing weight matching is more easily understood and implemented than true moment of inertia matching. Over the years, swing weight matching has become the de facto standard for club design. Consequently, it would be difficult to introduce a new set of golf clubs, wherein different golf clubs in the set exhibit different swing weights. It would also be difficult to introduce a set of golf clubs having swing weights that vary from the norm of D0 or D1 for men's clubs, or C5 to C7 for women's clubs.

However, it would be desirable to have a set of golf clubs which ‘feel’ the same through a wider range of movements during the golf swing. More specifically, it would be desirable to have a set of golf clubs that all exhibit the same moment of inertia during the release phase of the downswing, and also exhibit substantially the same translational inertia during other phases of the backswing and downswing. That is, it would be desirable to have the same ‘feel’ for all clubs during larger portions of the backswing and downswing movements.

SUMMARY

Accordingly, the present invention provides a set of golf clubs, wherein each golf club in the set exhibits substantially the same rotational moment of inertia about a fixed axis, and wherein each golf club in the set has the same translational inertia (i.e., total weight). That is, the golf clubs in the set are matched in both rotational moment of inertia and translational inertia. The present invention therefore includes the total weight of the golf club in the systematic matching of the golf clubs within a set.

In accordance with one embodiment, the total weight of each golf club is matched to the weight of the heaviest golf club of the set. For example, assuming that the 9-iron is the heaviest club of the set, then weight is added to each of the other clubs in the set, such that all of the clubs of the set weigh the same as the 9-iron. In order to prevent this added weight from significantly modifying the rotational moment of inertia of the clubs, the weight is added at the axis of rotation about which the rotational moment of inertia is determined and matched, either precisely or by approximation (e.g., by swing weight). In a particular embodiment, the weight is added inside the shaft of the club, at the grip end of the club.

The present invention will be more fully understood in view of the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the manner in which the swing weight of a golf club is determined.

FIG. 2 is a diagram illustrating an axis of translation exhibited while swinging the golf club of FIG. 1.

FIG. 3 is a diagram of a golf club having a weight installed in the shaft in accordance with one embodiment of the present invention, wherein the a swing weight or moment of inertia of the club is determined about an axis at the grip end of the club.

FIGS. 4A and 4B are diagrams illustrating the weight and shaft of the club of FIG. 3 in more detail in accordance with one embodiment of the present invention.

FIG. 5 is a diagram of a set of weight-matched golf clubs having a matched swing weight or moment of inertia about an axis located at the grip end of each club.

FIG. 6 is a diagram of a golf club having a weight installed in the shaft in accordance with an alternate embodiment of the present invention, wherein the a swing weight or moment of inertia of the club is determined about a axis away from the grip end of the club.

DETAILED DESCRIPTION

The present invention provides a matched set of golf clubs, wherein each club in a set of clubs, irons, woods, or a combination thereof has the same weight as other clubs in the set. This is done in a manner that minimally changes the overall moment of inertia of the club about a given axis of rotation. This can provide the golfer with a set of clubs wherein each club in the set has the same translational inertia (i.e., weight) as other clubs in the set as well as preserving the same rotational moment of inertia for all clubs in the set. This provides a more complete matching of the clubs within a set to a golfer's swing.

In accordance with the present invention, weight is added at or near the location of the rotational axis about which the moment of inertia (the rotational inertia) of each club in the set has been matched. The weight is added at this location to assure that the additional moment of inertia introduced by the weight is very small compared to, and does not significantly affect, the designed moment of inertia of the golf club.

The weight added is particular to each club in the set and is sufficient to bring the total weight of each club in the set up to the same desired total weight. For example, weight can be added to all but the heaviest club in the set, such that the total weight of each club is equal to the weight of the heaviest club in the set, thereby giving each club in the set the same translational inertia. Because the translational inertia (i.e., weight) of each club is matched, each club ‘feels’ the same during the last phase of the backswing and the initial phase of the downswing.

FIG. 3 is a diagram of a golf club 200 in accordance with one embodiment of the present invention. Golf club 200 includes shaft 201, club head 202, grip 203 and weight 205. In the absence of weight 205, the swing weight of golf club 200 is matched with the swing weight of other clubs in the same set (not shown). Consequently, golf club 200 and the other clubs in the same set are designed to have the same approximate moment of inertia about the axis A at the grip end of club 200. Alternatively, golf club 200 and the other clubs in the same set can be designed to have the same actual moment of inertia about the axis A. Weight 205 is affixed inside the grip end of shaft 201, in close proximity to axis A, in accordance with one embodiment of the present invention. More specifically, weight 205 is located as close as possible to the axis of rotation about which the moment of inertia of the clubs in the set is estimated or determined. Because weight 205 is located close to the axis A, this weight 205 has a minimal effect on the rotational moment of inertia of the club 200 about this axis A.

FIGS. 4A and 4B illustrate weight 205 and shaft 201 in more detail in accordance with one embodiment of the present invention. In this embodiment, weight 205 is a cylindrical weight of stepped diameter, with a large diameter section 205A having the same diameter as the outer diameter of the grip end of shaft 201, and a smaller diameter section 205B having a diameter slightly smaller than the inside diameter of the grip end of shaft 201. The smaller diameter section 205B is inserted into the grip end of hollow shaft 201. An adhesive layer may be applied between the outside of smaller diameter section 205B and the inside of shaft 201, thereby helping to hold weight 205 in place and prevent rattling. The large diameter section 205A extends a short distance beyond the end of the grip end of shaft 201. The large diameter section 205A prevents the weight 205 from slipping down the shaft 201 in the event the adhesive bond fails. Following installation of weight 205, the grip 203 is installed over the large diameter section 205A of the cylindrical weight and the grip end of shaft 201. Installation as described will minimize the additional moment of inertia contributed by the additional weight, thereby leaving the moment of inertia of the club nearly at its original value.

In other embodiments, weight 205 can have other shapes. For example, weight 205 can have threads which enable the weight to be screwed into the grip end of shaft 201. In other embodiments, weight 205 may include only large diameter section 205A or small diameter section 205B.

Weight 205 can be made of various materials, including, but not limited to, brass, aluminum, steel, lead, copper or other metals. In accordance with one embodiment, each club in the set may have a corresponding weight made of the same material. In another embodiment, different clubs in the set may have corresponding weights made of different materials. Thus, one club may have a brass weight, while another club may have an aluminum weight. In another embodiment, the weight material for each club is selected such that length of the weight used in each club of the set is substantially matched. That is, materials having different densities are used, such that each weight has the same (or approximately the same) length within each club. In another embodiment, the densest material that can be reliably fixed in the grip end of shaft 201 is used, thereby minimizing the effect the weight has on the moment of inertia of the club.

FIG. 5 is a diagram illustrating a small set of golf clubs, including clubs 200, 300, 400 and 500 in accordance with one embodiment of the present invention. Club 200 has been described above in connection with FIG. 3. In the described example, club 200 is a driver, although this is not necessary. Clubs 300, 400 and 500 have shafts 301, 401 and 501, respectively, club heads 302, 402 and 502, respectively and grips 303, 403 and 503, respectively. Club 500 is the heaviest club of the matched set. In the described example, club 500 is a 9-iron, club 400 is a 6-iron and club 300 is a 3-iron, although this is not necessary.

In the described example, each of clubs 200, 300, 400 and 500 has been swing weight matched, such that each of these clubs has the same estimated moment of inertia about axis A. In another embodiment, each of clubs 200, 300, 400 and 500 may be moment of inertia matched such that each of these clubs has the same actual moment of inertia about axis A.

Weights 205, 305 and 405 are inserted in the grip ends of shafts 201, 301 and 401 as illustrated. Weights 205, 305 and 405 are selected such that each of clubs 200, 300 and 400 weigh the same as club 500 (which does not include a weight). If all of the weights 205, 305 and 405 are made of the same material, then weight 205 will extend a greater distance into shaft 201 than weight 305 extends into shaft 301. However, this difference in distance has a minimal impact on the rotational moment of inertia of the clubs.

Note that weights 205, 305 and 405 will cause the swing weights of clubs 200, 300 and 400 to be significantly reduced (See FIG. 1). Thus, while clubs 200, 300 and 400 may have a swing weight of D0 or D1 without weights 205, 305 and 405, these clubs 200, 300 and 400 may have swing weights in the range of about A-3, B-8 and C-8 with weights 205, 305 and 405. Moreover, weights 205, 305 and 405 cause clubs 200, 300, 400 and 500 to have different swing weights (but the same feel). As described above, a relatively narrow range of swing weights are acceptable within the golfing community, and the swing weights associated with the present invention are significantly outside of this range. Thus, recognition that swing weight matching is only an approximation of moment of inertia matching, and that moment of inertia matching is the underlying design goal is required to make the improvements in club design represented by the present invention possible.

FIG. 6 is a diagram of a golf club 600 in accordance with an alternate embodiment of the present invention. Golf club 600 includes shaft 601, club head 602, grip 603 and weight 605. Golf club 600 is part of a set of golf clubs (not shown) which have the swing weight or moment of inertia determined about an axis B, which is located away from the grip end of the shaft 601. In this embodiment, the weight 605 is installed in the shaft 601, such that the center of mass of the weight 605 coincides as closely as possible to axis B. Again, weight 605 is selected to bring the total weight of the club 600 up to the desired level (i.e., the weight of the heaviest club in the set).

Although the invention has been described in connection with several embodiments, it is understood that this invention is not limited to the embodiments disclosed, but is capable of various modifications, which would be apparent to one of ordinary skill in the art. For example, although the present invention has described all golf clubs in a set as having the same weight, it is understood that in other embodiments, different subsets of golf clubs in the set can have different weights. For example, the long irons and woods of a set can be designed to have the same first weight, while the short irons of a set can be designed to have the same second weight, wherein the first weight is different than the second weight.

In addition, although the present invention has been described all golf clubs in a set having the same weight and same moment of inertia, it is understood that some variation in weights and moments of inertia may exist within a set, wherein the set still falls within the scope of the present invention. In one embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 10% range. Within this range, the weights of the clubs are defined as being “substantially equal”. In another embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 5% range. In yet another embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 1% range. 

1. A set of golf clubs comprising a first golf club having a first weight and a first moment of inertia about a first axis of the first golf club; a second golf club having a second weight and a second moment of inertia about a second axis of the second golf club, wherein the first moment of inertia is substantially equal to the second moment of inertia, and the first weight is substantially equal to the second weight.
 2. The set of golf clubs of claim 1, wherein the first axis is located at a grip end of the first golf club and the second axis is located at a grip end of the second golf club.
 3. The set of golf clubs of claim 1, wherein the first golf club comprises a first internal weight located inside a shaft of the first golf club at the first axis.
 4. The set of golf clubs of claim 3, wherein the first internal weight comprises an external portion which extends outside of the shaft of the first golf club.
 5. The set of golf clubs of claim 3, wherein the second golf club comprises a second internal weight located inside a shaft of the second golf club at the second axis.
 6. The set of golf clubs of claim 5, wherein the first internal weight is less than the second internal weight.
 7. The set of golf clubs of claim 3, wherein the first internal weight is a cylindrical weight.
 8. The set of golf clubs of claim 7, wherein the first internal weight is metal.
 9. The set of golf clubs of claim 7, wherein the cylindrical weight has a stepped diameter.
 10. The set of golf clubs of claim 1, wherein the first golf club has a first swing weight and the second golf club has a second swing weight, wherein the first swing weight is different than the second swing weight.
 11. The set of golf clubs of claim 1, wherein the first axis is located away from a grip end of the first golf club and the second axis is located away from a grip end of the second golf club.
 12. The set of golf clubs of claim 1, wherein the first weight and the second weight vary by 10% or less.
 13. The set of golf clubs of claim 12, wherein the first weight and the second weight vary by 5% or less.
 14. The set of golf clubs of claim 13, wherein the first weight and the second weight vary by 1% or less.
 15. A method of fabricating a set of golf clubs comprising: designing each golf club in the set of golf clubs to have substantially the same moment of inertia about a given axis; and adding weight to one or more of the golf clubs in the set at the given axis, such that each of the golf clubs in the set has the same weight.
 16. The method of claim 15, wherein the step of adding weight comprises affixing an internal weight inside a shaft of the golf club at the given axis.
 17. A method of fabricating a set of golf clubs comprising: designing each golf club in the set of golf clubs to have substantially the same swing weight; and adding weight to one or more of the golf clubs in the set at an axis about which the swing weight estimates a moment of inertia, such that each of the golf clubs in the set has the same weight.
 18. The method of claim 17, wherein the step of adding weight comprises affixing an internal weight inside a shaft of the golf club at the axis. 